void handle_arpreq(struct sr_instance *sr, struct sr_arpreq *req) {
time_t now = time(NULL);
if(difftime(now, req->sent) > 1.0) {
/* request timeout */
if(req->times_sent > 5) {
struct sr_packet *packets = req->packets;
/* iterate through all packets on queue */
while(packets) {
uint8_t *reply_packet = 0;
sr_ip_hdr_t *ip_hdr = (sr_ip_hdr_t *)(packets->buf+sizeof(sr_ethernet_hdr_t));
reply_packet = sr_generate_icmp((sr_ethernet_hdr_t *)packets->buf, ip_hdr, sr_get_interface(sr, packets->iface), 3, 1); /* create ICMP type 3, code 1 (host unreachable) */
/* if ICMP packet fails to generate */
if(reply_packet == 0) {
fprintf(stderr, "Error: failed to generate ICMP packet\n");
}
/* send ICMP packet to ip of packet in queue */
if(sr_send_packet(sr, reply_packet, sizeof(sr_ethernet_hdr_t) + sizeof(sr_ip_hdr_t) + sizeof(sr_icmp_t3_hdr_t), (const char*)(packets->iface)) == -1) {
fprintf(stderr, "Error: sending packet failed (handle_arpreq)");
}
packets = packets->next;
free(reply_packet);
}
sr_arpreq_destroy(&(sr->cache), req);
} else {
/* generate ARP packet */
struct sr_if *iface = 0;
/* if interface is not found */
if((iface = sr_get_interface(sr, req->packets->iface)) == 0) {
fprintf(stderr, "Error: interface does not exist (handle_arpreq)");
return;
}
uint8_t *arp_pkt = sr_new_arpreq_packet(NULL, iface->addr, req->ip, iface->ip); /* create ARP request packet to re-send */
/* send ARP request packet */
if (sr_send_packet(sr, arp_pkt, sizeof(sr_ethernet_hdr_t) + sizeof(sr_arp_hdr_t), (const char*)(iface->name))==-1) {
fprintf(stderr, "Error: sending packet failed.");
}
/* update arpreq fields */
req->times_sent++;
req->sent = now;
free(arp_pkt);
}
}
}
void sr_handleip(struct sr_instance* sr,
uint8_t * packet/* lent */,
unsigned int len,
char* interface/* lent */)
{
sr_ip_hdr_t *ip_hdr = 0;
struct sr_if *iface = 0;
sr_icmp_hdr_t *icmp_hdr = 0;
uint8_t *reply_packet = 0;
struct sr_rt *rt = 0;
uint32_t nexthop_ip, longest_mask = 0;
struct sr_arpentry *arp_entry = 0;
struct sr_arpreq *arp_req = 0;
sr_ethernet_hdr_t *ether_hdr = 0;
int matched = 0;
/* check if header has the correct size */
if (len < sizeof(sr_ethernet_hdr_t) + sizeof(sr_ip_hdr_t)) {
fprintf(stderr, "Error: invalid IP header length\n");
return;
}
ip_hdr = (sr_ip_hdr_t*)(packet + sizeof(sr_ethernet_hdr_t));
/* perform ip header checksum */
if (cksum(ip_hdr, ip_hdr->ip_hl) != 0xffff) {
fprintf(stderr, "Error: IP checksum failed\n");
return;
}
/* grab the receiving interface */
if ((iface = sr_get_interface(sr, interface)) == 0) {
fprintf(stderr, "Error: interface does not exist (sr_handleip)\n");
return;
}
/* if the packet is destined to our ip */
if (ip_hdr->ip_dst == htonl(iface->ip)) {
/* if it is an ICMP */
if (ip_hdr->ip_p == htons(ip_protocol_icmp)) {
/* check if header has the correct size */
if (len < sizeof(sr_ethernet_hdr_t) + sizeof(sr_ip_hdr_t) + sizeof(sr_icmp_hdr_t)) {
fprintf(stderr, "Error: invalid ICMP header length\n");
return;
}
icmp_hdr = (sr_icmp_hdr_t*)(packet + sizeof(sr_ethernet_hdr_t) + sizeof(sr_ip_hdr_t));
/* if it is an ICMP echo request, send an ICMP echo reply */
if (icmp_hdr->icmp_type == htons(8) && icmp_hdr->icmp_code == htons(0)) {
/* perform ICMP header checksum */
if (cksum(icmp_hdr, sizeof(icmp_hdr)) != 0xffff) {
fprintf(stderr, "Error: ICMP checksum failed\n");
return;
}
/* generate an echo reply packet */
if ((reply_packet = sr_generate_icmp((sr_ethernet_hdr_t *)packet, ip_hdr, iface, 0, 0)) == 0) {
fprintf(stderr, "Error: failed to generate ICMP echo reply packet\n");
return;
}
/* send an ICMP echo reply */
if (sr_send_packet(sr, reply_packet, sizeof(reply_packet), (const char*)interface) == -1) {
fprintf(stderr, "Error: sending packet failed (sr_handleip)\n");
}
free(reply_packet);
}
}
/* if it contains a TCP or UDP payload */
else {
/* generate Destination net unreachable (type 3, code 0) reply packet */
if ((reply_packet = sr_generate_icmp((sr_ethernet_hdr_t *)packet, ip_hdr, iface, 3, 3)) == 0) {
fprintf(stderr, "Error: failed to generate ICMP packet\n");
return;
}
/* send an ICMP */
if (sr_send_packet(sr, reply_packet, sizeof(reply_packet), (const char*)interface) == -1) {
fprintf(stderr, "Error: sending packet failed (sr_handleip)\n");
}
free(reply_packet);
}
}
/* packet not for us, forward it */
else {
/* if TTL reaches 0 */
if (ip_hdr->ip_ttl <= htons(1)) {
/* generate Time exceeded (type 11, code 0) reply packet */
if ((reply_packet = sr_generate_icmp((sr_ethernet_hdr_t *)packet, ip_hdr, iface, 11, 0)) == 0) {
fprintf(stderr, "Error: failed to generate ICMP packet\n");
return;
}
/* send an ICMP */
if (sr_send_packet(sr, reply_packet, sizeof(reply_packet), (const char*)interface) == -1) {
fprintf(stderr, "Error: sending packet failed (sr_handleip)\n");
}
free(reply_packet);
}
/* if packet has enough TTL */
else {
/* decrement the TTL by 1 */
ip_hdr->ip_ttl --;
/* recompute the packet checksum */
ip_hdr->ip_sum = htons(0);
ip_hdr->ip_sum = cksum(ip_hdr, sizeof(sr_ip_hdr_t));
/* Find entry in the routing table with the longest prefix match */
rt = sr->routing_table;
while (rt != NULL) {
/* update the gateway ip and the longest mask so far */
if ((rt->dest.s_addr & rt->mask.s_addr) == (ntohl(ip_hdr->ip_dst) & rt->mask.s_addr) &&
rt->mask.s_addr > longest_mask) {
nexthop_ip = rt->gw.s_addr;
longest_mask = rt->mask.s_addr;
matched = 1;
}
rt = rt->next;
}
/* if a matching routing table entry was NOT found */
if (matched == 0) {
/* generate Destination net unreachable (type 3, code 0) reply packet */
if ((reply_packet = sr_generate_icmp((sr_ethernet_hdr_t *)packet, ip_hdr, iface, 3, 0)) == 0) {
fprintf(stderr, "Error: failed to generate ICMP packet\n");
return;
}
/* send an ICMP */
if (sr_send_packet(sr, reply_packet, sizeof(reply_packet), (const char*)interface) == -1) {
fprintf(stderr, "Error: sending packet failed (sr_handleip)\n");
}
free(reply_packet);
}
/* if a matching routing table entry was found */
else {
/* if the next hop is 0.0.0.0 */
if(nexthop_ip == 0) {
nexthop_ip = ip_hdr->ip_dst;
}
/* set the source MAC of ethernet header */
ether_hdr = (sr_ethernet_hdr_t*)packet;
memcpy(ether_hdr->ether_shost, iface->addr, ETHER_ADDR_LEN);
/* if the next-hop IP CANNOT be found in ARP cache */
if ((arp_entry = sr_arpcache_lookup(&(sr->cache), htonl(nexthop_ip))) == NULL) {
/* send an ARP request */
arp_req = sr_arpcache_queuereq(&(sr->cache), nexthop_ip, packet, len, iface);
handle_arpreq(sr, arp_req);
}
/* if the next-hop IP can be found in ARP cache */
else {
/* set the destination MAC of ethernet header */
memcpy(ether_hdr->ether_dhost, arp_entry->mac, ETHER_ADDR_LEN);
/* send the packet */
if (sr_send_packet(sr, packet, sizeof(packet), (const char*)interface) == -1) {
fprintf(stderr, "Error: sending packet failed (sr_handlearp)\n");
}
free(arp_entry);
}
}
}
}
}
